Metal-working process and product



Patented Feb. 23, 1954 METAL-WORKING PROCESS AND PRODUCT Thomas I.McClintock, New Kensington, l a., and Alvin L. Hurst, Lafayette, Ind.,assignors to Aluminum Company of America, Pittsburgh, Pa., a corporationof Pennsylvania N Drawing. Application July 3, 1950, Serial No. 172,014

11 Claims. (01. 148-115) This invention relates to a method ofextrudingand cold working certain aluminous materials which creates acondition in the materials I that makes it possible to anneal them at alower temperature and the extruded and cold worked product having thatcharacteristic.

The extrusion process of shaping metal has been employed in the metalworking art for many years and it has been used very extensively in theproduction of aluminum articles and aluminumlbase alloys. As applied tothe manufacture of such aluminous products the process has generallyinvolved heating the metal body to be extruded to a high enoughtemperature to permit a ready flow of the metal, placing the body in aheated cylinder and forcing the metal out of a die mounted at one end ofthe cylinder. In extruding aluminum of commercial purity and thosealuminum base alloys which do not receive a precipitation treatment toincrease their strength it has been the practice to heat the metalbodies, usually ingots, to a temperature within the range of about 750to 1000 F. before inserting them in the cylinder of the extrusion press.

? The pressure applied during extrusion often causes some heating of themetal with the result that there is little, if any, cooling of the metalbody occurring during the course of the extrusion operation. Thetemperature to which the body is heated prior to extrusion is thereforeconsidered to be the nominal temperature of the metal during extrusionand is referred to as the extrusion temperature. The extrusion ofaluminum and aluminum base alloys within the temperature range of W50 to1000 F. is regarded as hot working as distinguished from working at roomtemperature, for example, which results in strain hardening. Theextruded product is usually allowed to cool to room temperature beforebeing subjected to any further fabricating operation.

In many cases the extruded article has the desired shape and no furtherworking is required;

however, it is often advantageous to produce a hardness are increased.If .a soft instead of a work hardened product is desired then the coldworked article must be annealed. Where the finished article is annealedthe treatmentv is referred to as a final annealwhereas if thereis to befurther working it is spoken of as an intermediate anneal.

As mentioned above, the effect of an annealing treatment is to decreasethe strength and hardness of the Worked article to a. minimum value.Hence, tensile tests can be used to reveal the progress of softening andwhen the strength,

elongation and hardness values reach a substantially constant minimum.it is considered that the material has been fully annealed. From thestandpoint of the internal structurev of the annealed metal it will befound that the treatment has caused the grain fragments produced byworking of the metal to form new grains or crystale that are free fromwork strains. When tensile tests show that a marked decrease in yieldstrength and increase in elongation have occurred the formation of newgrains has begun.

The temperatureat which new grains or crystals form is called therecrystallization temperfound in'rolled or forged articles. If thesemifinished extrusion is cold worked the strength and i loys.

ature. This temperature is not the same for all purities of aluminum andall aluminumbase al- The principal factors which control therecrystallization temperature are the composition of the metal, thelength of the period allowed for annealing and the amount of coldworking which the article has received immediately prior to annealing.However, for practical purposes in manufacturing operations it has beenfound that a temperature between 640 and 670 F. is required to effectrecrystallization of cold worked aluminum and aluminum base alloyswithin reasonable periods of time.

In the production of some articles it is highly desirable to have. avery low temperature of recrystallization. For example, where analuminum sheath has been cold drawn upon an insulated telephone or powercable'it is necessary to anneal the sheath to obtain the desiredflexibility in the cable. The conventional annealing temperature woulddestroy the usual insulation provided on cables. Hence, to soften thesheathing without damage to the insulation requires annealing at a. muchlower temperature.

The recrystallization of cold worked aluminum can be reduced, it hasbeen found, by controlling the iron to silicon ratio and by the additionof small amounts of at least one of the metals of the group composed ofberyllium and nickel. For convenience, these metals and others havingthe same effect may be here designated as recrystallization temperaturereducing alloy additions. The foregoing discoveries form the subjectmatter of co-pending applications Serial Nos. 172,001, 172,002 and172,003. It has now been found that the advantages of such compositionscan be more fully realized and the effect of the beryllium and nickelenhanced in the production of extruded and cold worked articles by thesteps described below. It is therefore a general object of thisinvention to provide a method of making articles having a lowrecrystallization temperature. A particular object is to enhance thischaracteristic in certain aluminum base alloy articles.

Our invention is based on the discovery that the recrystallizationtemperature can be reduced in extruded and cold worked aluminum basealloy articles consisting essentially of aluminum, an element whichreduces the recrystallization temperature, such as one selected from thegroup composed of 0.005 to 0.25% beryllium and 0.04 to 1% nickel, and atotal of 0.01 to 0.8% iron and silicon impurities, the ratio of iron tosilicon not exceeding 4/3 of the silicon content, and preferably only3/4 of the silicon content, by a preliminary treatment of the body to beextruded, extruding at a relatively low temperature, and intermediateannealing at a relatively low temperature where annealing is required,prior to cold working. Each of the steps affects the results obtained inthe succeeding operation and therefore it is only by close observance ofthe limitations on each step that the final product can be obtainedwhich has the desired low re crystallization characteristic. Theindividual steps in the process will now be described in greater detail.

The metal body, in the form of an ingot or a rolled or forged billet,having the proper chemical composition is given an initial thermaltreatment, called a preheat, followed by a controlled cooling to anintermediate temperature range and holding within this range for aperiod of time, prior to extrusion. The treatment consists of heatingthe body to a temperature between 850 and 950 F. and holding or soakingit with in this temperature range for a period from 1 to 12 hours. Thetemperature and length of the treatment will vary with the compositionof the alloy and the size of the load being processed.

Upon completion of the preheat or initial treatment the alloy body iscooled at a controlled rate, not exceeding 50 F. per hour, to atemperature within the range of 500 to 650 F. and maintaining the bodywithin this temperature range for a period of 1 to 12 hours. For thesake of convenience this may be referred to as an intermediate soakingtreatment. Following this the hot body may be cooled to room temperatureor it may be transferred to an extrusion press if the temperature of thebody is such as to permit extrusion within the range referred to below.The effect of the two thermal treatments is not altogether understoodbut both have been found to be necessary to obtain the lowrecrystallization characteristic in the final worked product.

If the body has been allowed to cool to room temperature, or atemperature below that at which it is to be extruded, the body is heatedto a temperature between 400 and 550 F, transferred to the heatedcylinder of an extrusion press and extruded. The temperature of themetal is considered to remain within this range during the extrusionprocess. It is desirable, in any case, to use as low an extrusiontemperature as possible, the temperature selected generally beingdetermined by the power of the press, more power being required as theextrusion temperature decreases. If extrusion temperatures above 550 F.are used, such as are normally employed in the extrusion of aluminum thedesired recrystallization characteristic in the final worked productwill not be obtained. The resulting semifinished extruded product isusually referred to as a bloom. It may be a solid or a hollow shapedepending on the die used. The combination of preheating, intermediatesoaking and extrusion at a low temperature establishes a condition andinternal structure in the bloom which is essential to obtaining a lowrecrystallization temperature in the subsequent cold worked article.

The extruded bloom is then subjected to further working at a much lowertemperature, usually at room temperature or slightly above it. Theworking may consist of rolling, drawing, pressing or similar operationswhich effect a reduc- N tion in the thickness of the article. In makingtubular products a machine may be employed known as a tube reducer. Itis to be understood that the working may be conducted in one or moresteps and with one or more types of working operations employed insuccession. In any event, if the final product is to be produced at thisstage, i. e., reduced to final shape and thickness, the reduction shouldamount to at least 40% and for the best results it should exceed if thebenefits of a low recrystallization temperature are to be realized.

If the preceeding operation is not a final working step, the cold workedproduct may then be given an intermediate annealing within thetemperature range of 400 to 600 F. from 1 to 12 hours. It has been foundto be necessary to use such a relatively low temperature range forintermediate annealing to insure a low recrystallization temperature inthe finally fabricated article.

After the intermediate anneal the article should receive further coldworking which produces a reduction in thickness of the article of atleast 40% and preferably more than 90% to obtain the benefit of areduced temperature of recrystallization. This working may include twoor more working operations. In the case of tubing, for example, theoperations may consist of drawing and sinking. Since sinking producesbut slight change in wall thickness the drawing must be relied upon toprovide most of the required cold working.

The article which has received the foregoing cold work and the properthermal treatment will have the capacity to recrystallize at a lowertemperature than the same article fabricated by conventional procedures.In general, the temperature of recrystallization will be below 600 F.and in many cases it will be less than 450 F.

One application of this invention is to be found in the provision of aseamless sheath for an insulated telephone cable. The effects ofpreheating and extrusion temperatures upon the tensile properties of asheath are illustrated in the following tests.

The fabricating schedule of the sheaths were identical except forvariations in the preheating practice and the reheating for extrusion.The constant factors were the size of ingot, rate of extrusion, colddrawing the extruded bloom with a reduction of about 61%, annealing at460 to 480 F. for 12' hours, and further cold drawing to a tube having0.460" O. D. andv 0.050" wall thickness with a reduction of 95% Thefinal cold drawn sheath was then annealed at 375 F. for A hour tosimulate the treatment which might be used on an insulated cable. Thetensile properties of the final annealed product were determined whichprovided a comparison with the other annealed products to show theeffects of varying the preheating practice and the extrusiontemperature. The alloy employed consisted of aluminum, 0.01% beryllium,0.03% iron and 0.04% silicon. The tubular ingots had an O. D. of 9" andI. D. of 11%".

In the first tests designed to determine the eiiect of preheating andintermediate soaking the ingot, one ingot was not preheated, but merelyheated to the extrusion temperature of 510 F. while the other one waspreheated 2 hours at 880 to 900 R, cooled slowly, at less than 50 F. perhour, to 580 to 600 F. and held at that temperature for 4 hours. The.tensile properties of the cold drawn and annealed sheaths are given inthe table below.

, TABLE I Efiect of preheating on properties of sheathing Tensile YieldPercent Ingot Condition slgelslgih, stgezsigtli, ElongationNon-preheated 16, 800 15. 200 7. Preheated 10, 200 5-, 900 17. 0

It is quite apparent that the preheating and intermediate soaking hashad a very pronounced effect upon the tensile properties. The low valuesexhibited by the sheath made from the preheated ingot indicate thatrecrystallization had occurred.

The influence of the extrusion temperature upon the tensile propertiesof annealed sheathing is illustrated in tests in which two ingotsreoeived the preheating and intermediate soaking treatments describedabove. One ingot was extruded at 905 F., which is in the range oftemperatures normally used in extruding aluminum of commercial purityand the other one was heated to 510 F. and extruded. The tensileproperties of the final products appear below in Table II.

TABLE II Efleet of extrusion temperature on properties of sheathingTensile Yield Percent Extrusion Temp. Elongation 'truded'irom ingotswhich did not receive these treatments. This is illustrated in Table IIIby the strength and elongation values of the tubular bloom, 2%" O. D.with a wall thickness of 0.433, from which the sheathing was producedreferred in Table I.

These test results and others have demon.- strated that preheating,intermediate soaking and a low extrusion temperature have a definitebeneficial effect upon the blooms and hencethe blooms possessdistinctive characteristics. not found in the usual extruded product.

Having thus described our invention and certain embodiments thereof, weclaim:

1. The process of producing aluminous. metal extrusions having lowtemperature recrystallization characteristics when cold workedcomprising providing a body consisting essentially of aluminum, a totalof 0.01 to 0.8% iron and silicon impurities, the amount of iron notexceeding 4/3 of the silicon content, and an element selected from thegroup composed of 0.005 to 0.25% beryllium and 0.04 to 1% nickel,heating said body to a temperature between 850 and 950 F., holding saidbody at said temperature for a period of 1 to 12 hours, cooling saidbody to a temperature between 500 and 650 F. at a controlled rate notexceeding 50 F. per hour, holding said body within said temperaturerange for a period of 1 to 12 hours, and thereafter extruding it at atemperature between 400 and 550 F.

2. The process of producing aluminous metal extrusions having lowtemperature recrystallization characteristics when cold workedcomprising providing a body consisting essentially of aluminum, a totalof 0.01 to 0.8% iron and silicon impuriti the amount of iron notexceeding 4/3 of the silicon content, and an element selected from thegroup composed of 0.005 to 0.25% beryllium and 0.04 to 1% nickel,heating said body to a temperature between 850 and 950 holding said bodyat said temperature for a period of 1 to 12 hours, cooling said body toa temperature between 500 and 650 F. at a controlled rate not exceeding50 F. per hour, holding said body within said temperature range for aperiod of 1 to 12 hours, cooling it to room temperature, reheating saidcooled body to a. temperature between 400 and 550 F. and extruding it.

3. The process of producing cold worked aluminous metal extrusionshaving low tempera.- ture recrystallization characteristics comprisingproviding a body consisting essentially of aluminum, a total of 0.01 to0.8% iron and silicon-impurities, the amount of iron not exceeding 4/3of the silicon content, and an element selected from the group composedof 0.005 to 0.25% beryllium and 0.04 to 1 nickel, heating said body to atemperature between-850 and 950 F., holding said body at saidtemperature for a period of l to 1.2 hours, cooling said body to atemperature between 500 and 650 F at a controlled ratenot exceeding 50F. per hour, holding said body within said temperature range for aperiod of 1 to 12 hours, extruding said heated body at a temperaturebetween 400 and 550 F. to form a bloom, and cold working the extrudedbloom at least 40 l 4. The process of producing cold worked aluminousmetal extrusions having low temperature recrystallizationcharacteristics comprising providing a body consisting essentially ofaluminum, a total of 0.01 to 0.8% iron and silicon impurities, theamount of iron not exceeding 4/3 of the silicon content, and an elementselected from the group composed of 0.005 to 0.25% beryllium and 0.04 to1% nickel, heating said body to a temperature between 850 and 950 F.,holding said body at said temperature for a period of 1 to 12 hours,cooling said body to a temperature between 500 and 650 F. at acontrolled rate not exceedin 50 F. per hour, holding said body withinsaid temperature range for a period of 1 to 12 hours, cooling it to roomtemperature, reheating said cooled body to a temperature between 400 and550 F., extruding said heated body at a temperature between 400 and 550F. to form a bloom, and cold working the extruded bloom at least 40%.

5. The process of producing cold worked aluminous metal extrusionshaving low temperature recrystallization characteristics comprisingproviding a body consisting essentially ol aluminum, a total of 0.01 to0.8% iron and silicon impurities, the amount of iron not exceeding 4/3of the silicon content, and an element selected from the group composedof 0.005 to 0.25% beryllium and 0.04 to 1% nickel. heating said body toa temperature between 850 and 950 F., holding said body at saidtemperature for a period of 1 to 12 hours, cooling said body to atemperature between 500 and 650 F. at a controlled rate not exceeding 50F. per hour, holdin said body within said temperature range for a periodof l to 12 hours, extruding said heated body at a temperature between400 and 550 F. to form a bloom, cold working the bloom, annealing saidworked article at a temperature between 400 and 600 F. for a period of 1to 12 hours and further cold working the article at least 40 6. Theprocess of producing cold worked aluminous metal extrusions having lowtemperature recrystallization characteristics comprising providing abody consisting essentially of aluminum, a total of 0.01 to 0.8% ironand silicon impurities, the amount of iron not exceeding 3/4 of thesilicon content, and an element selected from the group composed of0.005 to 0.25% beryllium and 0.04 to 1% nickel, heating said body to atemperature between 850 and 950 F., holding said body at saidtemperature for a period of 1 to 12 hours, cooling said body to atemperature between 500 and 650 F. at a controlled rate not exceeding 50F. per hour, holding said body within said temperature range for aperiod of 1 to 12 hours, cooling it to room temperature, reheating saidcooled body to a temperature between 400 and 550 R, extruding saidheated body to form a bloom, cold Working said bloom, annealing saidworked article at a temperature between 400 and 600 F. for a period of 1to 12 hours and further cold working the article at least 90% 7. Theprocess of producing aluminous cable sheathing having a low temperaturerecrystallization characteristic comprising providing an ingotconsisting essentially of aluminuma total of 0.01 to 0.8% iron andsilicon impurities, the amount of iron not exceeding 4/3 of the siliconcontent, and an element selected from the group composed of 0.005% to0.25% beryllium and 0.04 to 1% nickel, heating said ingot to atemperature between 850 and 950 R, holding the ingot at said temperaturefor a period from 1 to 12 hours, cooling said ingot to a temperaturebetween 550 to 650 F. at a rate not exceeding 50 F. per hour, holdingsaid ingot within said temperature range for a period of 1 to 12 hours,thereafter extruding said ingot to tubular bloom form at a temperaturebetween 400 and 550 F., cold drawing said bloom, annealing the colddrawn tube at a temperature between 400 and 600 F. for a period of l to12 hours, and further cold drawing said annealed tube at least to formthe sheathing.

8. An extruded bloom which when cold worked at least 40% can berecrystallized at a temperature below 600 F., said bloom consistingessentially of aluminum, 0.01 to 0.8% total iron and silicon impurities,the iron not exceeding 4/3 the silicon content and an element selectedfrom the group composed of 0.005 to 0.25% beryllium and 0.0 1 to 1%nickel, said bloom having an internal structure resulting frompreheating the body from which the bloom is formed at a temperaturebetween 850 to 950 R, cooling said body at a rate not exceeding 50 F.per hour to a tem-- perature between 500 and 650 holding the body withinthis temperature range and extruding it at a temperature between 400 and550 F.

9. An extruded bloom which when cold worked at least 90% can berecrystallized at a temperature below 450 F., said bloom consistingessentially of aluminum, 0.01 to 0.8% total iron and silicon impurities,the iron not exceeding 3/ l of the silicon content and an elementselected from the group composed of 0.005 to 0.25% beryllium and 0.04 to1% nickel, having an internal structure resulting from preheating thebody from which the bloom is formed at a temperature between 850 and 950F., cooling said body at a rate not exceeding 50 F. per hour to atemperature between 500 and 650 F., holding the body within thistemperature range and extruding it at a temperature between 400 and 550F.

10. An extruded and cold worked article consisting essentially ofaluminum, 0.01 to 0.8% total iron and silicon impurities, the iron notexceeding 4/3 of the silicon content and an element selected from thegroup composed of 0.005 to 0.25% beryllium and 0.04 to 1% nickel, saidarticle having an internal structure resulting from preheating the bodyfrom which an extruded product is formed to a temperature between 850and 950 F., cooling said body at a rate not exceeding 50 F. per hour toa temperature between 500 and 650 holding thebody within thistemperature range, extruding it at a temperature between 400 and 550 F.,and finally cold working at least 40%, and characterized by its capacityto recrystallize below 600 F.

11. An extruded and cold drawn cable sheath consisting essentially ofaluminum, 0.01 to 0.8% total iron and silicon impurities, the iron notexceeding 3/4 of the silicon content, and an'element selected from thegroup composed of 0.005 to 0.25% beryllium, and 0.04 to 1% nickel, saidsheath having an internal structure resulting from preheating the bodyfrom which an extruded bloom is formed to a temperature between 850 and950 F., cooling said body at a rate not exceeding 50 F. per hour to atemperature between 500 and 650 F., holding the body within thistemperature range, extruding it at a temperature between 400 and 550 F.,cold drawing the extruded product, intermediate annealing said colddrawn article between 400 and 600 F., and further cold drawing thearticle with a reduction of at least 90%, and characterized by itscapacity to recrystallize below 450 F.

THOMAS I. McCLINTOCK.

ALVIN L. HURST.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 2,218,459 Singer Oct. 15, 1940 i0 FOREIGN PATENTS NumberCountry Date 211,027 Great Britain Feb. 18, 1924 6 OTHER REFERENCESMetals Handbook, 1948 ed., pp. 769-771. Transactions of the AmericanSociety for Metals, vol. 41, 1939, pp. 443-459.

Grain Control in Industrial Metallurgy, l0 publ. by American Society forMetals, 1949, pages

1. THE PROCESS OF PRODUCING ALUMINOUS METAL EXTRUSIONS HAVING LOWTEMPERATURE RECRYSTALLIZATION CHARACTERISTICS WHEN COLD WORKEDCOMPRISING PROVIDING A BODY CONSISTING ESSENTIALLY OF ALUMINUM, A TOTALOF 0.01 TO 0.8% IRON AND SILICON IMPURITIES, THE AMOUNT OF IRON NOTEXCEEDIING 4/3 OF THE SILICON CONTENT, AND AN ELEMENT SELECTED FORM THEGROUP CONSISTING OF 0.005 TO 0.25% BERYLLIUM AND 0.04% TO 1% NICKEL,HEATING SAID BODY TO A TEMPERATURE BETWEEN 850 AND 950* F., HOLDING SAIDBODY AT SAID TEMPERATURE FOR A PERIOD OF 1 TO 12 HOURS, COOLING SAIDBODY TO A TEMPERATURE BETWEEN 500 AND 650* F. AT A CONTROLLED RATE NOTEXCEEDING 50* F. PER HOUR, HOLDING SAID BODY WITHIN SAID TEMPERATURERANGE FOR A PERIOD OF 1 TO 12 HOURS, AND THEREAFTER EXTRUDING IT AT ATEMPERATURE BETWEEN 400 AND 550* F.